On Monday, the court heard arguments around the question of whether the penalty prescribed by the ACA to individuals who have not obtained health insurance is actually a tax. If it is a tax, then the Anti-Injunction Act would bar a review of the law’s constitutionality until the provision actually goes into effect in 2014. Most observers of the court appeared to agree that both conservative and liberal justices do seem to judge the ACA as a whole and would likely issue a ruling that the penalty is not actually a tax.

On Tuesday the court studied the constitutionality of the individual mandate provision in the ACA. From the transcript it is clear that Solicitor General Donald Verilli faced extremely skeptical questions and the justices spent considerable time trying to find what they called a “limiting principle” (e.g. a reason that the federal government’s power to intervene in the market was both necessary and that it would be constrained).

The final arguments both took place on Wednesday, with time devoted to the question of “severability” – what part, if any, of the ACA could survive if the court ruled that the individual mandate was indeed unconstitutional. The choices ranged from striking just the individual mandate all the way to the idea that the entire law should be struck. In the afternoon the court heard arguments about the constitutionality of the Medicaid expansion scheduled to take effect on January 1st, 2014. Essentially the states argued that the federal government’s expansion of Medicaid, even the offer to pay for most of it, is so large that it is coercive, leading to the compromise of the state’s own sovereignty. Again, the aggressive questioning seemed to confirm that the conservative justices might be tempted to strike down that part of the law. Lyle Denniston, a long time court reporter, observed that such a ruling would sacrifice the Medicaid expansion that serves the needy “to a historic expression of judicial sympathy for states’ rights.” Click here to read more.

It is nearly impossible to predict the final outcome of these arguments. Although the justice’s questions during oral arguments occasionally telegraph an outcome, it is also true that cases are not dependent on the oral arguments themselves, particularly in a well briefed case such as this one. Perhaps what is now clear is that it is indeed possible that the justices might decide the law is unconstitutional. Perhaps given the tone of politics and the strong opposition to the law, thisshould not be too surprising. Yet many legal observers, including me, argued that the law was likely to be upheld. (See this video for more details.)

Justice Anthony Kennedy is likely to be the 5th vote either to uphold the law or to strike it down. Certainly it was clear from the questioning that he has the potential to rule against it. Yet at the end of the arguments regarding the individual mandate, Kennedy also seemed to come up with his own definition of a limiting principle, one that would allow him to uphold the law. For now, the only thing to do is wait – the ruling will likely be out by the end of June.